1. Field
Example embodiments relate to optical touch screen apparatuses and methods of driving the optical touch screen apparatuses.
2. Description of the Related Art
A touch screen is a device through which input data is directly received via a screen such that a touch by a person or by a pen on a position of a display screen is detected to be processed by software. To this end, a touch screen is formed by attaching a touch panel to a display panel to implement the above function. Examples of the touch panels are resistive overlay type, capacitive overlay type, surface acoustic wave (SAW) type, infrared beam type, and piezoelectric type touch panels. Recently, touch screens are widely used in various fields as input devices for replacing a keyboard or a mouse.
Touch screens are operated by touching a display device directly with a finger or by using a pen. However, as the size of display devices gradually increases, and a distance between the user and the display device is increased, the direct touching method may be difficult to apply. An optical touch screen, which performs the same function as touch screens, senses light instead of a touch by a finger or a pen. The optical touch screen is expected to be advantageous not only for communication between a user and a terminal but also for communication between users.
In order to implement an optical touch screen, a micro-sized light sensing device which is capable of sensing light is required. A typically used light sensing device is an amorphous silicon thin film transistor (a-Si TFT). However, in an a-Si TFT, a variation in current caused by light is not sufficiently large. Accordingly, charges that are generated in a photodiode when light is applied are accumulated in a capacitor for a predetermined period of time, and then a signal regarding light intensity is generated based on the amount of charges accumulated in the capacitor. However, when using the capacitor, parasitic capacitance may increase as the size of the optical touch screen increases.